A wheel of a vehicle is mounted to a chassis of the vehicle by an axle. To ensure smooth rotation of the wheel about the axle, lubricant, such as grease and lubrication oil, is commonly applied between the wheel hub and the axle. The lubricant is usually preserved in a cup. Two types of lubricant cups are known. One includes visual inspection means for allowing a user to visually check the amount of the lubricant in the cup and the other does not.
A major problem encountered by the lubricant of the axle is emulsification. Once emulsified, the grease or lubrication oil deteriorates and loses its function of lubrication thereby causing damage to the axle.
FIG. 1 shows a conventional oil cup indicated by reference numeral 1. The oil cup 1 comprises a casing with a vent hole 111 defined therein for pressure balance and heat dissipation purposes. The vent hole 111, however, also provides a leaking passage for water to get into the cup, especially when the vehicle is cleaned with pressurized water or when the vehicle is moving across a river. Water getting into the oil cup 1 through the vent hole 111 is mixed with and emulsifies the grease or lubrication oil contained therein.
Thus, it is desired to provide an oil cup that is capable to effectively block water from leaking into the oil cup thereby eliminating the emulsification of the oil contained therein.